XBEE positioning: Collect RSSI value from several XBee routers...how?

My question has been asked few years ago, but with confusing answers: http://www.digi.com/support/forum/34267/collect-rssi-value-from-several-xbee-routers-how

So I will reiterate the question carefully:
What we have:
=== One FIXED coordinator (C)
=== three FIXED routers (R1,R2,R3)
=== MOVABLE End devices (ED1, ED2, …)

What we need (for the purpose of positioning):
RSSI(ED1<>R1) value is 200 --|
RSSI(ED1<>R2) value is 120 --| Three values obtained at “real-time”/within short period.
RSSI(ED1<>R3) value is 50 ----|

 RSSI(ED2&lt;&gt;R1) value is 200  --|
 RSSI(ED2&lt;&gt;R2) value is 120  --| Three values obtained at "real-time"/within short period.
 RSSI(ED2&lt;&gt;R3) value is 50 ----|


RSSI value reported by module only represents RSSI of last hop. If a transmission spans multiple hops, the DB value provides no indication of the overall transmission path, it only indicates the quality of the last link.

It may be the case that both transmission followed same hopping path and thus similar RSSI values are reported.